Hygroscopic material and method of preparing the same



Patented May 14, 1935 PATENT OFFIC l IYGROSCOPIC MATERIAL AND METHOD OF PREPARING THE SALE Albert J. Loepcinger and William M. Trafton,

Providence, R. 1., assignors to American Moistenlng Company, Providence, R. 1., a corporation of Maine No Drawing.

Application July 17, 1931,

Serial No. 551,519 2 Claims. (Cl. 297-l) This invention relates to hygroscopic material and methods of preparing the same. More especially the present invention involves the discovery that material made from elastic tissue is unexpectedly eifective as a humidity responsive element in that it has well-nigh perfect hygroscopic properties, is extremely sensitive and is rel ably accurate.

In the art of humidification there has been a keen desire for a material which is aiertly responsive to humidity changes and whose reactions thereto can be employed to control apparatus which humidifies or to indicate or record the humidity conditions in the atmosphere. Such material as wood, fabrics, parchment, hair and catgut have been employed but with only partial success because they suffer from serious inherent faults which render them more or less unreliable.

Apparatus employing such materials are some-.

what sluggish in operation, work with a characteristic hunting" action and frequently require calibration due to the sensitive material becoming stretched or distorted and acquiring a perma nent set.

The invention gives to the art a material which is free from all the objections noted as inherent to substances previously used, and possesses in addition distinctive properties of its own that make it extremely useful and well adapted for the purposes described. Its accuracy in response to humidity changes is maintained throughout the full range of temperatures and humidities of factory-working or domesticrliving conditions. It is particularly accurate and alertly responsive in the upper ranges of relative humidity, say above 65%, commonly needed for certain textile processes where wet and dry bulb instruments are likely to become increasingly sluggish and inaccurate because of the near approach of the wet and dry temperatures, and where other hygroscopic materials become weak, easily stretched and generally distorted because of their limp condition.

The material of the invention is not adversely affected by prolonged exposure either to extremes of temperature or of .humidity. It may remain dry and inactive over a week-end or longer period of plant shut-down and immediately resume its hygroscopic function when called upon to do so and without attention or adjustment of the apparatus with which it is associated. On the other hand it may be limp and sodden when the air surrounding it is saturated for a long period and still respond promptly when less humid conditions again prevail. Experience shows that this layers.

reliability continues through many months of use, or of disuse, and is apparently permanent.

One convenient source of obtaining the material of the invention is the cecum of an ox. This is made up of several layers of tissue, the middle layersof which may be termed layers of elastic tissue being for the most part made of fibers composed of a peculiar substance called elastin. This substance more nearly-resembles rubber than any other substance found in tissue and one would ordinarily be misled by this resemblance to assume that it has, like rubber, no appreciable hygroscopic properties.v We have discovered, however, that this substance, or perhaps more generally speaking, that elastic tissue is unexpectedly effective as a hygroscopic material and that its efiectiveness can be increased by the elimination or removal of other tissue which may initially be associated with it.

In the case of the cecum of the ox, for example, the initial step in the preparation of the desired material is the separation of the outer layers of the cecum from the middle or elastic This is accomplished by scraping. The remaining tissue is then treated chemically to rid the elastic layer of the collagenous fibers remaining after the scraping.

A dilute solution of potassium hydroxide, such as a 0.25% aqueous solution, removes a. considerable portion of the collagenous fibers but this reaction must be allowed to take place slowly and is preferably carried out for only short periods of time with intermittent washing in distilled water.

A 1% of pepsin aqueous solution having a pH value of 4.6 at 375 C. may be employed to remove the collagenous fibers and will do so in a much shorter time than does potassium hydroxide but in using the pepsin as a digestant there is danger of the elastic fibers themselves being attacked. This may be almost entirely avoided if the material is not treated with the pepsin solution for a period exceeding one hour.

After either the pepsin or potassium hydroxide treatments the remaining tissue is repeatedly washed with distilled water until all of the reagents used have been completely removed. The wet membranes are then stretched on a frame and allowed to dry. It is then cut into strips or sheets of the size required for its adaptation to the apparatus with which it is to be associated.

It is preferred to use the membrane of elastic tissue under mild tension in the form of a strip, associated with means for continuously drawing to it a sample of the air whose hygrometric conditions are to influence the membrane. The membrane possesses ample strength throughout the range of humidities common in the arts and its dimensional response to varying humidity is so large that a short length working in conjunction with a simple lever is all that is ordinarily needed for a regulator of surpassing sensitivity.

It is a further feature of the material of the invention that it does not attract or hold dust, lint or' fine particles of size which are usually present in the atmosphere, particularly in a textile establishment. This may be explained by the fact that the membrane has no sensible moisture on its surface and by the fact that it is capable of assuming either a positive or negative charge 01' static electricity. This last fact is not of great importance for the quantity of the electric charge on the membrane is so minute that it has little influence in repelling lint or dust coming against it. It is believed 'that the reason why particles do not stick to the material is primarily due to its physical condition rather than to any electric charge which it may carry.

Tests and actual use of the material have confirmed the discovery that the material possesses unexpectedly superior hygroscopic properties. Under as like conditions as was possible to attain, humidifiers controlled by the hygroscopic material of the invention have started and stopped several times more often than when controlled by a wet and dry bulb regulator. A characteristic chart record of relative humidity in a room controlled by a regulator employing the material oi! this invention as the sensitive element, is commonly a smooth line, whereas previously it has been a succession of hills and dales or serrations. Thus the unusual sensitivity of the material has been established.

The continued use of the material under varying"and at times extreme conditions with no apparent change in its accuracy has proven it to be entirely reliable. Apparatus employing the material when once adjusted requires no subsequent calibration and no attention so far as cleaning of the sensitive element is concerned.

The unusual sensitivity together with the unprecedented reliability of the material enables results to be achieved which have not heretofore been deemed attainable. It is now possible to maintain a desired humidity within a variation of less than three quarters 01' one per cent. This is a most noteworthy increase of efllciency in the art of controlling humidity.

We claim:

1. A hygroscopic element for humidity responsive apparatus, consisting of a piece of animal membrane composed substantially of elastin.

2. A hygroscopic element for humidity responsive apparatus, consisting 01' a piece of animal membrane from which the collagenous material and material other than the elastic tissue has been substantially all removed, leaving .as the hygroscopic material the said elastic tissue.

ALBERT J. LOEPSINGER. WILLIAM M. TRAFTON. 

